Telegraph key



' Jur ae 6, 1944.

TELEGRAPH KEY H. E. TROMHOLT Filed Oct. 15, 1942 IF-FIE- 2.

2 Sheets- Sheet 1 IN V EN TOR.

Mam flora/3M June 6, 1944. H. E. TROMHOLT TELEGRAPH KEY Fi led Oct. 15, 1942 2 Sheets-Sheet 2 FIE/4w INVENTORH Patented June 6, 1944 UNITED. STATES OFFICE-.1.

2,350,481 i I TELEGRAPHKEY Hans EiTro'mholt, Bayside;LongoIslandgN."Y.2. I Application-betcha:15, 1942 Serial .Nii'. 462,'099

2 Claims. (Cl. 178 -101 1 This .inventionarelates-to telegraph:keys'andi particularly .it refers .to: a key. of :such .construc.-; tionzthat the noise generated by the.- operation-hf same is reduced to a point below. the: audible-level;-

sound generated by the rapid-manual operation of *thekey. Most commercially available keys make such a loud noise that they can easily be heard from one room-t the" next and it was found inthe last war thatquite often'spies would listen in on secret tele raphic dispatches'm'erely' by'listening to the noise of the. keys from-an adjoining room." Anothendifiiculty has been due a to the fact thatkeysordinarily'have' not been electrically insulated so-that-the operator would receiveshocks fromithe handle bar in thunder storms and when, forinstance, ,accidentlyisom'e high voltage were introduced in" the telegraph circuit. In my present invention I have'elimi nated this. situation andI have provided a key which is electrically insulatedand nearly noise-1 less, or. which in technical termsmaybe saidpto have hadits noise level reduced to below the audible minimum. This audibl'eminimum is also oftendesignated as the .threshhold 'cflhearing, which is the noise level at which a normal human ear can no longer distinguish a given sound.

The object of my invention is, therefore, to provide a noiseless telegraph key Another object of my invention is to provid'ea key whi'chis compact, light, dependable inoperation, and.low

In the drawings, wherein for the purpose of illustration, is shown a' preferred embodiment. of

my-. invention,. the) numeral I 0, designates the knob, which is-mounted on thearm .l l.. The arm I l is .provided with .a transverse shaft. I 2,.which is pivoted: in two bearings .I3 .inthe. .Ushaped bracket .l 4;-- which .is mounted on the. base. l 5. The arm lil furthermore is providediwith-anadjustablescrew l6; which has-a locknutrlland a spring-. -l 8,: which is recessed .in i base I 5. The spring;.gi8 serves .to hold the; arm I! in. the-upward position eat: alltimes except: when: pressed downwardbythe operatorbyplacing his hand onknob iJ.--' The. U shaped-bracket. M is .mounted to base=|5- by means of counter-bored screws l9.- Thezhole-inbase:lfiginzwhich screws l9 are placed is -afterwards ffillediin'with insulating. compound. The: based-5511163 a lpluralityaofz mounting-holes. ZELand is ialsoactinglasi-the support for the tar-- minals 2liandsfi2awhiclrzareinormally,-the input terminals ineasingle circuit...;key;- Th'e armpit which carries the knob:lc at onexend carries at itsiother end-themetalmember-Zii; which is electrically :insulatedfrom arm-1 i: by -meansof insu latedtstri-ps 24 aand insulating tubings 255 The member-23is fastened to arm' H by meansofscrews 26 and- 2l; see-Figure Screw- 26 extends :through the member 23 "and is furnished with nut '28 under which is placed" the soldering terminaliQg-whic-h is electrically connected by means of=theflexiblewire 30 to the inputterminal 2i: The outer' end of the" metallic member' 23 carries the electrical" contact 3 I g which extend through said member 23"and has a contact surface on both sides of "same: The contact mem ber' 3i il'I'filJS '--norma1, non-operative position, makes contact "withithe lower contact screw 32; which is fastened in the base .lErby means of nut 33:,fsee Figure4. At oneendiof'the base ldis mountedthe Z laped bracket 341 which fcarries. the upper con-. tactlsci'ew 35.with.the contact point ,3$."" The screw 35 is adjustable intth'e bracket 342w means oflock nut 31. Bracket fie'lis mounted to the base. i5; by ,means of screw 38;l'theupper endof which is furnished witlf'nut Zit under which is fastened soldering. terminal 22; see: Figure 3..

The tlife .and-. satisfactory operational? the key is depending ,toa considerable extent upon the bearings l3 ,and the transverse- -shaft. l2. 1 It shouldbe snoted tthereforethat :the shaf-t l2 is pinnedato the armtl-t-by'means of pin 48 andthe shaft i2 is usually made from phosphor bronze or other suitable material, while the bearings l3 may be either stainless steel or may be ball bearings. This construction will greatly increase the useful life of the key and will prevent same from wearing and becoming loose and unreliable in operation. It should, furthermore, be noted that with this construction it is not necessary to adjust the bearings as is usually required by the heretofore commonly used telegraph keys,

which in most cases have pivot type bearings. The operation of my invention is as follows:

In using the present key, the connections'are made to'term'mals 2| and 22 in the usual man-' ner. The contact adjustment screw 35 is adjusted to give the minimum'required gap'between the contact point 36 and the contact 3| of the member 23. After the screw 35 hasbeen once adjusted it is locked infplaceby the lock" and 36. The member 23 is, furthermore, clamped bythe screw 26 and 21 in such a manner that it could only vibrate with its free end, which is very short. To prevent the transmission of nut 31 and will not have to be adjusted again for a long time depending upon the service for acoustical insulation is meant that the insulat-' ing parts 24 and the tubular members 25 are placed in such a manner and are selected of such materials that audible vibrations generated by the, clicking of the contacts'3l and 36 will not be transmitted from the member, 23 to the arm II. It is 'a well-known fact that sound orin more technical language, acoustic vibra-. tions, will travel through metals atvery high speeds and..depending upon the frequency of the sound transmitted,,the vibrationsmay exe citethe metal parts into forced vibrations of a similar or harmonic ,frequency, It is ,wellknown too that every structural part, regardless whethersame is madefrom metal or other elastic material, has a certain natural frequency which is usually called its resonant frequency and at which it will vibrate violently if excited. When a sound wave is transmittedthrough an elastic body, such as a metal part it will travel at great speed until it hits a boundary medium. At this point it will set up what is usually called an acoustic impedance, which may be very great depending upon the nature ofthe boundary me- I dium. This acoustic impedance will usually transmita small part of the on-coming sound wave, while the'rest 'of the wave will be reflected back toward its origin. By applying'the correct acoustic insulation, therefore, to obtain aii'ac'oustic impedance'of a 'suitablemagnitudefthesoundwave may be reflected in its entiretyandiio transmission of same will result. In thisevent, the sound will travel back and forth and'will dissipate itself in the form of heat. In the event, however, that the member through whichthe sound wave'is travelling "has a *resonant freany sound waves from the member 23 to the arm I l and to other parts connected with same,

7 I have provided the insulation 24 and 25, which effectively provides a high acoustic impedance, stopping any sound waves generated in member 23. By selecting the insulation 24 and 25 from suitable material, such a fibre, Bakelite, or other fibrous substances, I can thereby prevent the transmission of any sounds from the member 23 to the other parts of the key, particularly to the arm I I, which would naturally have a fairly low resonant frequency and would be able to carry out audible vibrations if so excited. i It is to be understood that the form of my invention, herewith shown and described, is to be taken as a preferred example of th same and that various changes in the shape, size, and arrangement of parts may be resorted to, without departing from the spirit of my invention or the scope of the subjoined claims.

Having thus. described my invention I claim: 1.]A telegraph key of the character described, comprising'a base; a bearing support mounted on said base, a plurality of bearings mounted in said bearing support; an arm pivoted intermediate of its ends in said bearings and having a knob mountedon one end; a contact making member fastened to the other end of said arm, said contacting making member being straight, short and rigid and projecting a small distance from the end of said arm and'having a considerable cross section as compared to its length, whereby same will have a high natural vibrating frequency, and acoustical insulation placed between said contact making member and said arm,

quency inside of the range of the sound'wave V or its harmonics,- the member maybe excited into-forced vibrations'of an 'audible character. To avoid this it'is only necessarytodesign-a member of such" physical size and characteriswhereby audible vibrations created in said member may be dissipated in same without being transmitted 'to'said arm.

2. A telegraph key of the character described, comprising a pivoted arm having a knob at one end; a contact makingmember fastened to and projecting slightly from the other end of said am, said contact making. member being short and rigid and attached by more than one point to said arm and said points of attachment being longitudinally of said arm and tending to give said contact making member a high natural'vibration frequency, and acoustical and electrical insulation provided between said contact making member and said arm,whereby sounds-generated in said contact making member may be confined to and dissipated in same without bein HANS E. 'IROMHOLT. i 

